1. Field of the Invention
The present invention relates to an engine braking control system for automotive automatic transmissions, being capable of applying engine braking as well as wheel braking, during braking operation.
2. Description of the Prior Disclosure
Recently, there have been proposed and developed automotive automatic transmissions having an engine braking control system. One such automatic transmission has been described in Japanese Patent First Publication (Tokkai) Showa 56-39349.
In the aforementioned conventional engine braking control systems, a shift solenoid is activated or deactivated so as to control application of engine braking, depending on the ON and OFF states of a brake switch applied for detecting depression of a brake pedal. Down-shift operation for an automatic transmission is executed as the shift solenoid becomes ON when the brake switch becomes ON under a fully closed state of a throttle valve. In this manner, since a braking requirement is monitored through the brake switch, engine-braking is necessarily applied, as soon as the brake switch becomes ON.
However, in such conventional engine braking control systems, since a brake switch is applied for monitoring depression of a foot-brake pedal, the brake switch will become ON even by a slight depression of the brake-pedal and thereafter a shift solenoid will be activated. As set forth above, engine braking may be applied by a slight depression of the brake-pedal before application of the foot-brake. This results in an uncomfortable feeling for braking operation.
Furthermore, in such conventional engine braking control systems, during quick braking operation, an excessively great braking force may be applied to vehicle wheels due to the sum of braking forces generated by both of the foot-brake and engine braking and therefore the wheels are rapidly decelerated. Under these conditions, there is a tendency for wheel-lock to occur.